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Investigating the effect of pollution on freshwater invertebrates, using Mayfly Nymph as an indicator. Background Information Pollution can be defined as "adding to the environment a potentially hazardous substance or source of energy faster than the environment can accommodate it." Freshwater pollution Organic waste, such as sewage is often dumped into rivers, as it is the easiest way to get rid of it. If the discharge of organic waste is small compared to the amount of water in the river, then it is broken down to simple in organic substances by bacteria and fungi, a process known as self-purification. If however the discharge becomes too much, bacteria thrive and begin to use up oxygen from the river, this causes a biological oxygen demand. (B.O.D) Eutrophication Eutrophication means nutrient enrichment. The main factor that causes eutrophication is the heavy use of nitrogen fertilisers and the increase in discharge of phosphates from sewage works. Nitrates and phosphates are...

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